Does Slow Processing Speed Cause Dyslexia?

Many kids with dyslexia read slowly. I find this in my clinical work, when I use tests such as the Gray Oral Reading Test 5 (GORT 5), the Test of Word Reading Efficiency – 2 (TOWRE-2), and the Reading Fluency Subtest of the Woodcock Johnson – III Tests of Achievement. If you have taken the time to sit and read aloud with a child who is dyslexic, and you may have found it to be downright painful. The process of decoding what one is reading and to sound out words generally makes this a slow process for these children, and most parents and teachers want to help them along as soon as they get stuck. Some of these children who read slowly do other things slowly, too. Can slow processing speed cause dyslexia?

Dyslexia (or Specific Learning Disability in Reading as it is officially defined in the DSM-V) can have many causes, one of which is slow processing speed. Slow processing speed appears to be a large factor for many kids who struggle with reading and is one part of the “double-deficit” theory of dyslexia. The other component, poor phonological awareness, is often considered the most common symptom in dyslexia.

Kids with poor phonological awareness struggle to recognize and manipulate the sound structure of words. In simpler terms, these kids may lack the awareness of the many letter sounds in language. For example, they might not hear or, more precisely, recognize the sound the letter “t” makes or be able to use that sound in reading a word. Phonological awareness is a foundation for decoding words in which readers need to connect sounds to letters, such as knowing that the letter “t” makes the “tuh” sound.

It is interesting to note that kids who fit the double deficit theory of dyslexia process other information slowly, as well. And kids who show signs of slower processing speed and poor phonological skills will be poorer readers than those who show only one of these deficits.

Psychologists use a variety of measures to assess the type of slow processing speed that is implicated in dyslexia. Most common is the use of “rapid naming tests,” where children are asked to name rapidly a series of familiar items such as colors, shapes, common objects, letters, or numbers presented on a page. Performance on more general tests of processing speed such as those used in IQ testing and in evaluating executive functions are also correlated with reading difficulties.

Slow processing speed is also a predictor of difficulty with reading comprehension. Consider how much more difficult it is to remember and understand what you are reading if it takes a long time just to read the words. Even beyond the length of time needed to sound out words, the intensity of cognitive effort required for reading fluency leaves limited resources to comprehend what children with dyslexia have read. For these children, it is as if they had to overexert themselves while hiking a spectacular mountain range, leaving them little energy to appreciate their experience.

One hidden impact of slow processing speed on reading is social/emotional. Studies suggest that children who have difficulty with slow processing speed tend to be more anxious, struggle in areas of social competence and self-esteem, and display weaker adaptive skills. The hidden consequences of slow processing speed and dyslexia suggest interventions beyond a resource reading class in school, including a multi-modal approach to treatment that entails the use of an intensive reading program such as Orton-Gillingham or Wilson, cognitive behavior therapy for self-esteem, and social skills training to address interpersonal competencies.

Here at the LearningWorks for Kids blog, there is much more information to be found on dyslexia, slow processing speed, and other learning challenges. Does your child suffer from dyslexia and slow processing speed? What interventions have been most helpful for you? Let us know below in the comments.